MICROSTRUCTURE OF FEPT PT MAGNETICTHIN FILMS WITH HIGH PERPENDICULAR COERCIVITY/

Microstructures of 50 nm thick FePt magnetic thin films deposited on P t buffer layers with various thicknesses (0-500 nm) grown on a Fe seed ed MgO (100) substrate have been studied by transmission electron micr oscopy to correlate them with magnetic properties. High density of pla nar defects such as twin and antiphase boundary are present in the FeP t films. The twins observed in these films are not the {011} twins whi ch are commonly observed in the bulk FePt magnet, but they are the {11 1} twins. The density and morphology of these twins drastically change depending on the composition of the FePt thin films as well as the th ickness of the Pt buffer layer, while that of the antiphase boundary d oes not show noticeable changes. In the Pt buffer layer, a high densit y of dislocations is present in order to reduce the elastic strain due to a large lattice mismatch imposed between the Pt layer and the MgO substrate (about 9%). When the thickness of the Pt buffer layer is inc reased to 500 nm, the Pt and FePt layers show a polycrystalline micros tructure having a grain size ranging from 0.3 to 2.0 mu m. The origin of the magnetic hardness is discussed based on these microstructural o bservation results. (C) 1998 American Institute of Physics. [S0021-897 9(98)09120-8].